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The photodegradation of ceftriaxone (CFT) in aqueous solution induced by UVB irradiation was studied in the presence and in the absence of oxygen. These selected conditions simulate some natural situations of contaminated water, where dissolved oxygen and the fraction of UV radiation that penetrates the terrestrial atmosphere could participate in the photodegradative process. CFT undergoes unimolecular photodegradation when irradiated with UVB light, and in an oxygen atmosphere the photodegradation process increases due to the action of reactive oxygen species (ROS), which are generated by photosensitization processes that involve the CFT triplet excited state (3CFT*). We report here for the first time the transient absorption spectrum, the lifetime and the quantum yield of 3CFT*. In the photodegradative mechanisms, hydroxyl radicals, superoxide radical anions and hydrogen peroxide are generated and participate in the CFT photooxidation. Bioassays on the Vero cell line demonstrated that the CFT photoproducts generated in the presence and in the absence of oxygen are not cytotoxic. A decrease in the bactericidal capacity of CFT after UVB exposure against S. aureus strains was also observed. The photoproducts obtained under photooxidation mechanisms mediated by ROS suffer a greater loss of antimicrobial activity. These results, from an ecological point of view, are very interesting since the action of UVB light represents an adequate method for natural CFT degradation in water because it allows a decrease in the generation of multi-resistance to antibiotics by bacteria. Also, the presence of photolysis products does not show toxic effects on living organisms. [ABSTRACT FROM AUTHOR]

Including the effect of the molecular environment in the numerical modeling of time-resolved electronic spectroscopy remains an important challenge in computational spectroscopy. In this contribution, we present a general approach for the simulation of the optical response of multichromophore systems in a structured environment and its implementation as a quantum algorithm. A key step of the procedure is the pseudomode embedding of the system-environment problem resulting in a finite set of quantum states evolving according to a Markovian quantum master equation. This formulation is then solved by a collision model integrated into a quantum algorithm designed to simulate linear and nonlinear response functions. The workflow is validated by simulating spectra for the prototypical excitonic dimer interacting with fast (memoryless) and finite-memory environments. The results demonstrate, on the one hand, the potential of the pseudomode embedding for simulating the dynamical features of nonlinear spectroscopy, including lineshape, spectral diffusion, and relaxations along delay times. On the other hand, the explicit synthesis of quantum circuits provides a fully quantum simulation protocol of nonlinear spectroscopy harnessing the efficient quantum simulation of many-body dynamics promised by the future generation of fault-tolerant quantum computers.

Molecular excitons play a major role within dye aggregates and hold significant potential for (opto)electronic and photovoltaic applications. Numerous studies have documented alterations in the spectral properties of dye homoaggregates, but only limited work has been reported for heteroaggregates. In this article, dimeric dye stacks were constructed from azobenzene-like dyes with identical or distinct structures, and their excitonic features were computationally investigated. Our results show that strong exciton coupling is not limited to identical chromophores, as often assumed, based on a recently made available Frenkel Exciton Hamiltonian and multiconfigurational plus second-order perturbation theory energetics methodology. Heteroaggregate stacks were found to exhibit different absorption features from the corresponding interacting monomers, indicating considerable coupling interactions between units. We analyzed how such coupling may vary according to various aspects, such as the relative positions of the interacting monomers or the differences in their energetics. Such qualitative and semiquantitative analyses allow the evaluation of the excitonic behavior of these dye aggregates to encourage further efforts toward a deeper understanding of the excitonic properties of tailored dye heteroaggregate systems.

The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations.